It is known to prepare carboxylic acids from carboxylic acid esters at elevated temperatures in liquid or vapor phase in the presence of various catalysts. G.B. Patent No. 1,286,700 teaches the liquid phase hydrolysis of allylic acetate in the presence of water in a molar ratio of 1:1 to 1:10 at a temperature of from 150.degree. to 350.degree. C., under pressure to yield allyl alcohol and acetic acid. Allyl alcohol is removed as it is formed by distilling it overhead. Hydrolysis conditions are selected to minimize the reversible reaction of the allyl alcohol with acetic acid to form the allyl ester. Pressure is at least 5 atmospheres gauge. British Patent No. 1,100,561 teaches the vapor phase hydrochlorolysis of methyl acetate with hydrochloric acid in the presence of a catalyst comprising zinc chloride on kaolin to produce acetic acid and methyl chloride. Methyl chloride is removed as it is formed by distillation. Japanese Kokai No. 78 31,608 (CA89:59664k) teaches gas phase hydrolysis of methyl acetate to acetic acid and methanol in presence of water with SiO.sub.2 --Al.sub.2 O.sub.3 catalysts at 150.degree.-300.degree. C.
Other processes are known for preparation of acetic acid compounds from esters of acetic acid. U.S. Pat. No. 1,872,479 teaches a process for producing acetic anhydride from ethylene diacetate by a cracking process in which vapor of ethylene diacetate is suddenly subjected to a high temperature, i.e., between 300.degree. and 450.degree. C., without use of catalysts for a period of 1 to 2 seconds. U.S. Pat. No. 2,730,546 teaches a process for preparing acetic anhydride from methyl acetate in the presence of a mixture of carbon monoxide and hydrogen, N-methyl pyrrolidone and a complex cobalt halide catalyst at a pressure of 200 atmospheres and 180.degree. C. for 15 hours. U.S. Pat. No. 2,789,137 teaches a process for preparing acetic anhydride from methyl acetate in the presence of N-methyl pyrrolidone, cobalt iodide and a mixture of carbon monoxide and hydrogen, at a pressure of 700 atmospheres and a temperature of 190.degree. C. The reaction required 17 hours.
In the oxidation of para-xylene to terephthalic acid, large quantities of acetic acid are used as solvent. Methyl acetate is formed as a by-product of the oxidation and purification process. Quantities of methyl acetate produced by the para-xylene oxidation process are large. A simple gas-phase process which would regenerate acetic acid from methyl acetate and reduce acetic acid losses to a minimum is highly desirable.
An object of this invention is to provide an improved process for preparation of a carboxylic acid from a carboxylic acid ester of the formula RCH.sub.2 COOR"' or R'CH:C(R")COOR"' wherein R, R' and R" are individually selected from the group consisting of --H, alkyl moieties of 1 to 18 carbon atoms, and aralkyl moieties, cycloalkyl moieties and alkylaryl moieties of from 3 to 18 carbon atoms, and wherein R"' is an aliphatic moiety of 1 to 18 carbon atoms.
An object of this invention is to provide an improved process for the continuous catalytic hydrolysis of methyl acetate in the vapor phase.
A further object of this invention is to provide an improved process for hydrolysis of methyl propionate in the vapor phase.
These and other objects are achieved by the invention in accordance with which the vapor phase preparation of carboxylic acids from carboxylic acid esters of the formula RCOOR"' and R'CH:C(R")COOR"' wherein R, R', R" and R"' are defined as heretofore, including specifically alpha-, beta-unsaturated carboxylic acid esters, is carried out in the presence of a catalyst comprising a borosilicate crystalline molecular sieve, designated as AMS-1B, having the following composition in terms of mole ratios of oxides: EQU 0.9.+-.0.2M.sub.2/ nO:B.sub.2 O.sub.3 :YSiO.sub.2 :ZH.sub.2 O
wherein M is at least one cation, n is the valence of the cation, Y is a value within the range of 4 to about 600, and Z is a value within the range of 0 to about 160, and providing a specific X-ray diffraction pattern.
Esterification and hydrolysis are reversible reactions, depending on reaction conditions. Molecular sieves have been used in the esterification of carboxylic acids. H. R. Harrison, et al., Chem & Ind, November 1968, P 1568, teaches use of molecular sieves to selectively adsorb water from a mixture of water and methanol to allow direct isolation of the methyl ester from the esterification reaction by distillation. Sulfuric acid is the catalyst. Heinz, Z.Chem. 1978, 18(1), 22-3 (Chem.Abst., 88, 120584g) teaches the esterification of acetic acid with alcohols using zeolites. Y. T. Eidus, et al., U.S.S.R. Patent 615,060 (Chem. Abst., 89, 108192r) teaches preparation of C.sub.3 -C.sub.6 alkyl esters of C.sub.3 -C.sub.7 carboxylic acids using X- or Y-type zeolites containing Rh, Pd, Co or Ni cations at 240.degree.-250.degree. C. and increased pressure. However, molecular sieves comprising a borosilicate crystalline molecular sieve, designated as AMS-1B, have not been previously taught as catalysts for preparation of carboxylic acids from carboxylic acid esters.